.. code-block:: python

	#!/usr/bin/env python
	# -*- coding: utf-8 -*-
	
	
	from __future__ import print_function
	import pymzml
	import get_example_file
	
	def main():
	    """
	    Accessing positive or negative polarity of scan using obo 1.1.0
	
	    usage:
	
	        ./polarity.py
	
	    """
	    example_file = get_example_file.open_example('small.pwiz.1.1.mzML')
	    run = pymzml.run.Reader(
	        example_file,
	        obo_version = '1.1.0',
	    )
	    for spec in run:
	        negative_polarity = spec['negative scan']
	        if negative_polarity is None:
	            negative_polarity = False
	        if negative_polarity == '':
	            negative_polarity = True
	        positive_polarity = spec['positive scan']
	        if positive_polarity is None:
	            positive_polarity = False
	        if positive_polarity == '':
	            positive_polarity = True
	        else:
	            positive_polarity = False
	        print(
	            'Polarity negative {0} - Polarity positive {1}'.format(
	                negative_polarity,
	                positive_polarity
	            )
	        )
	        exit(1)
	
	    return
	
	if __name__ == '__main__':
	    main()
